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Biology in America 



tain the same number and kinds of atoms, the latter are 

 differently arranged in the molecules. Such molecules dif- 

 fering in the arrangement of their component atoms, are 

 known by the somewhat formidable term of stereoisomers. 

 Miescher has shown that serum albumen for example has a 

 possibility of 1,000,000,000 stereoisomers. Now if nuclein has 

 one-tenth as many and if each determiner in the human 

 chromosome consists of but a single molecule of nuclein, the 

 number of possible arrangements within the nucleus of the 

 fertilized egg becomes so great as to be wholly beyond the 

 range of human ken. 





PHOTOGRAPHS OF CHROMOSOMES 



From an insect magnified 1,500 times. The pair of sex chromosomes 

 is shown at x in Fig. 3. In Figs. 14 and 15, which show the chromo- 

 somes divided into two groups, each of which passes into a new cell, 

 the larger one of the pair, which " determines " the female sex, is seen 

 passing to the lower group. After Wilson, ( ' Journal of Experimental 

 Zoology," Vol. 6. 



Still stronger evidence of the behavior of the chromosomes 

 as outlined above is afforded by that of the sex chromosomes, 

 which have been found in a large and ever increasing number 

 of animals. Like the devils in the herd of swine on the 

 shores of Galilee, the number of hypotheses regarding the 

 cause of sex, which have in times past infested the human 

 mind, is legion. As early as the eighteenth century Drelin- 

 court enumerated 262 untenable theories of sex determination, 

 and as Blumenbach aptly said, "Drelincourt's theory formed 

 the 263rd." Since then, possibly as many more sex theories 

 have blossomed and withered without bearing fruit. Recent 

 investigation indicates that sex determination is in Nature's 



